feat(checker): cph-check orchestrator + cph-cli cph binary (WU-5)

Closes the core pipeline: the `cph` CLI checks an engineering file and compiles
a PDF.

cph-check — phases (a) load → (b) structural (known-kind set) → (c) schema →
(d) typst compile → (e) render-coverage. Compile is gated: skipped if (a)-(c)
produced any Error (broken input would only add noise); `check` compiles every
declared target (dedup identical diags), `build` compiles the one requested.
Render-coverage emits a non-blocking RenderIgnored *warning* when a (kind,
target) has no render rule — severity pinned via RENDER_IGNORED_SEVERITY const
citing spec Diagnostic.renderIgnoredSeverity + ADR-0005. No double-emit:
unknown/missing parts are skipped downstream. API: check(root, engine) ->
CheckReport, build(root, engine, target) -> (Option<pdf>, CheckReport).

cph-cli — clap: `cph check <path>` (exit 1 on any Error, warnings → 0) and
`cph build <path> --target <name> [-o out]` (default target student, default
out <path>/build/<target>.pdf). Diagnostics → stderr via Display, results →
stdout. --render-dir override.

End-to-end on examples/TH-141 (39 parts): `check` → 0 errors/0 warnings;
`build` → real PDF student 9pp/395KB, teacher 12pp/474KB. Broken-element check
(unclosed delimiter in a stmt.typ) → span-accurate
`error[E-TYPST-COMPILE]: unclosed delimiter --> lemmas/…/stmt.typ:7:8`, exit 1.
Workspace: fmt + clippy -D warnings + test all green.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/cph-cli/Cargo.toml

@@ -9,3 +9,7 @@ name = "cph"
 path = "src/main.rs"
 
 [dependencies]
+cph-check = { path = "../cph-check" }
+cph-diag = { workspace = true }
+cph-typst = { path = "../cph-typst" }
+clap = { version = "4", features = ["derive"] }